1. Field of the Invention
This invention relates to impact modification of poly(alkylene terephthalates).
2. Description of the Prior Art
Although impact modifiers for poly(alkylene terephthalates) based on rubbers of polybutadiene, butadiene-styrene copolymers, butadiene-acrylonitrile copolymers, ethylene-propylene rubbers, polyisobutene and polyisoprene have been suggested, no one has suggested impact modifiers based on acrylic rubbers which are multi-phase composite interpolymers. See, for example, U.S. Pat. No. 3,919,353. Although such acrylic rubber-based composite interpolymers have been suggested as impact modifiers for thermoplastic polymers in general, they have especially been suggested for vinyl halide polymers and acrylic polymers.* It was unexpected that such impact modifiers should also function well to modify poly(alkylene terephthalates) because acrylic polymers and vinyl halide polymers are both considered amorphous plastics whereas poly(alkylene terephthalates), especially poly(butylene terephthalate), are generally considered to be a crystalline plastics. It would be considered unexpected to those skilled in the art that the modifiers and techniques used to obtain enhancement of specific properties in one plastic can be extended to the other plastic. FNT * See Owens U.S. Pat. No. 3,808,180
Combination impact modifier melt strength improvers based on multiple stage polymers having an epoxy functional final stage have been disclosed by Lane, Ser. No. 631,761 filed Nov. 13, 1975 now U.S. Pat. No. 4034013. Lane's materials operate by significantly increasing melt viscosity. However it is frequently desired by processors of poly(alkylene terephthalates), especially in injection molding of PBT, to achieve impact modification without significantly increasing melt viscosity.